DE 10 2004 008 265 A1 discloses a method for motor vehicles having a wheel slip control system, which has means for detecting wheel slip on one or more vehicle wheels, a wheel slip controller, which generates one or more wheel-specific control variables, and one or more actuators, which serve for adjusting the wheel slip by the wheel-specific control variable. For improving the control system, at least one wheel-specific control variable of the wheel slip controller is adjusted by a correction variable, representing the wheel normal force on the corresponding wheel, to a new control variable for the actuators.
Known traction controllers seek to set a target slip of the drive wheels through engine and braking interventions. Here the known traction controllers take the form of two independent controllers, that is to say the brake controller and the drive engine controller. Both controllers set their slip targets using the actuators available. For this purpose the brake controller relies exclusively on the brake actuator and the drive engine controller exclusively on the drive engine actuator. Since the brake controller and the drive engine controller may have different slip targets, the controller having the lowest slip target setting usually takes precedence.
The traction controller described above having two independent controllers for the brakes and the drive engine may lead, when both controllers are active, to the following problems. Owing to the isolation of the two controllers, the controllers are only capable of a delayed reaction to the interventions of the other controller. This can therefore result in both controllers overreacting in order to achieve their slip targets. Although the state of the art discloses corrections and complex rules to take account of the various dependent functions of the variables involved and to balance the two controllers, the benefit of these is only limited, owing to the fundamental disadvantages of a controller design having two independent controllers for the brakes and the drive engine. Furthermore, these corrections and complex rules are complicated to program in and thereby unmanageable. In addition, different slip targets of the two controllers may mean that the controller having the higher slip target has a tendency to abandon the control prematurely, because its target slip is greater than that of the other controller. Without the intervention of the controller having the higher slip target setting, however, the controller having the lower slip target cannot attain its target. A stationary operating point close to the minimum target slip setting is therefore often not located. This leads to unnecessary control interventions, which may sometimes be disturbing or uncomfortable for the driver.
The object of the invention, therefore, is to provide a method for traction control and a traction control system, which overcomes the aforementioned disadvantages.